Otl's with AvantGarde Duos?

It seems to me the primary goal of an OTL is to eliminate hysteresis loss and bandwidth limiting imposed by output transformers. Since David Berning's patent is about another approach to achieve that goal, may I suggest that the results are all that count. In the conventional sense Ralph is right, but it may be irrelevant if someone is able to invent a better mousetrap - but that's not to say the other is. An amplifier with zero hysteresis loss between the output tubes and the binding posts by virtue of no iron in the signal path and no output transformation in the audio band can, in a practical sense, be considered to be output transformerless due to the same benefits it delivers. Just my opinion, sprinkle liberally with salt, film at eleven, etc. Bottom line, use your ears to see which you prefer. Both are outstanding amplifiers.

Brian

Rushton, sorry but you are right, I don't get it!

Please explain.

I was equally polite in showing Ralph that he's not right in his terminology of the Berning design.

There is much, much more to it than that.

Essentialaudio, yes, exactly but again it's even more complicated than that because there is no such thing as a Zero Hysteresis Audio bandwidth output transformer, if Dave invented such a thing, he would instantly be rich :)

It's not an Audio output transformer, there are lots of transformers in the Berning design but none are Audio bandwidth output transformers.

It's certainly nowhere close to a conventional OTL, which is what should be said and correct but not that it has output transformers and Semiconductor outputs, which is not true.

The comment that Ralph made in regards to me having admitted that the ZOTL is not an Output-Transformerless amplifier in PF magazine is incorrect. What I stated is something to the effect that the ZH270 is full of transformers, but none are output (or audio) transformers. In fact, except for a small DC-blocking capacitor at the input of the amplifier, the ZH270 is DC-coupled, an impossibility for any audio transformer-coupled amplifier.

David Berning

Hi David, could you then explain the presence of the air core transformer in the output section of your amplifier? Seems to me that a rose by any other name is still a rose. So I guess what I want to know is how the air core transformer shown is not in fact a transformer in the output section.
As I read the patent, it seems to play a crucial role in the design.

Also, you *did* mention in PF some years back when this issue first appeared (in a letter to the editor) that people did not seem to understand the idea of zero hysteresis loss, and found it easier to understand when you told them it was an otl instead. I can dig the quote up for you if you like. Anyone with back issues of PF can find it.

This was a bit after the time that Harvey Rosenberg was promoting your amplifier in his reviews, having negotiated a contract with you to sell your amps. So that would make it in the 1997-1999 period. Harvey told me that at the '98 CES and you told me that the contract had expired at the '98 Philadelphia Triode Show. So I know the timeframe is correct.